We've just finished installing an OM606 into a W123 pickup truck(see signature). Everything is coming together but we aren't sure what people do about the wastegate. We know it's vacuum actuated but we don't know what needs to be done to switch over to a pressure actuated wastegate or if there's another simple option.

Hy,
U can convert the original k14 to pressure actuated waste gate, like any other turbo. But there was reasons behind having a vacum actuator.
Anyhow, it will work fine most of the times.
If want to know more PM me.